Change default make behavior to O3 optimization

Makefile

@@ -5,24 +5,27 @@ else
 V := @
 endif
 
-# Debugging
-ifeq ("$(DEBUG)","0")
-D :=
-else
-D := -g
-endif
-
 # Optimizations
-ifeq ("$(OPTIMIZE)","1")
+ifeq ("$(OPTIMIZE)","0")
+O := -O0
+else ifeq ("$(OPTIMIZE)","1")
 O := -O1
 else ifeq ("$(OPTIMIZE)", "2")
 O := -O2
 else ifeq ("$(OPTIMIZE)", "3")
 O := -O3
 else
-O := -O0
+O := -O3
 endif
 
+# Debugging
+ifeq ("$(DEBUG)","1")
+D := -g
+else
+D :=
+endif
+
+
 SRC_DIR=src
 INCLUDE_DIR=include
 BUILD_DIR=build